The present invention relates to a process for producing 1,1,1,5,5,5-hexafluoroacetylacetone with high purity, which is useful as a raw material for producing medicines, agricultural chemicals and low-boiling-point chelate compounds used in the process for manufacturing electric parts.
H. Gilman et al., J. Am. Chem. Soc., Vol. 78, pp. 2790-2792 (1956) teaches a process for producing 1,1,1,5,5,5-hexafluoroacetylacetone, which is shown by the following reaction formulas: 
A. Henne et al., J. Amer. Chem. Soc., Vol. 69, pp. 1819-1820 (1947) discloses a process for producing anhydrous 1,1,1,5,5,5-hexafluoroacetylacetone by turning a sodium salt of 1,1,1,5,5,5-hexafluoroacetylacetone into a copper chelate compound, then recrystallizing the copper chelate compound, and then removing the copper with hydrogen sulfide.
R. Haszeldine et al., J. Chem. Soc. London, 1951, pp. 609-612 discloses that a reaction liquid is treated with dilute sulfuric acid and then extracted with ether, and the resulting organic layer is distilled to obtain distillates over the range 36-90xc2x0 C. It is disclosed therein that the portion of boiling point 85-90xc2x0 C. appears to be 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate.
H. Gilman et al., J. Am. Chem. Soc., Vol. 78, pp. 2790-2792 (1956) further discloses the precipitation of 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate by concentrating an organic layer extracted with ether.
In general, raw materials, including 1,1,1,5,5,5-hexafluoroacetylacetone, for producing medicines, agricultural chemicals and electronic parts are required to have higher purity, as compared with raw materials for other uses.
It is therefore an object of the present invention to provide a process for producing 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate with high purity, which is an intermediate for 1,1,1,5,5,5-hexafluoroacetylacetone.
According to the present invention, there is provided a first process for purifying a crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate containing an impurity. The first process comprises bringing said crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate into contact with a poor solvent, thereby removing said impurity from said crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate. In the specification, xe2x80x9cpoor solventxe2x80x9d means an organic solvent in which 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate is substantially insoluble.
According to the present invention, there is provided a second process for purifying a crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate containing an impurity. The second process comprises precipitating crystals of 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate from a specific solution of said crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate.
The process for producing a crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate, which is to be purified by the first or second process of the invention, is not particularly limited. For example, such crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate can be produced, as follows. At first, a reaction vessel is charged with a reaction solvent and a base. Then, a mixture of 1,1,1-trifluoroacetone, a trifluoroacetic acid ester and a solvent is gradually added to the reaction vessel with stirring or the like to homogenize the reaction mixture, while the reaction mixture was maintained at a predetermined temperature lower than the reaction temperature. Then, according to need, the temperature of the reaction vessel is raised to accelerate the reaction, thereby forming a salt of 1,1,1,5,5,5-hexafluoroacetylacetone.
In the process for producing a crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate, the reaction vessel may be made of glass, fluororesin or a material lined with one of these. The reaction solvent may be an ether having a boiling point preferably of about 30-140xc2x0 C. Examples of such ether are diethyl ether, dibutyl ether, t-butyl methyl ether, diisopropyl ether, and tetrahydrofuran (THF). The base may be an inorganic base. Examples of this inorganic base are alkali metals and alkali earth metals, alkoxides of such metals, and hydrides of such metals. More concrete examples are sodium methoxide, sodium ethoxide, sodium hydride, sodium, potassium methoxide, potassium ethoxide, potassium hydride, potassium, and lithium hydride. The trifluoroacetic acid ester is not particularly limited, since its ester moiety acts as a leaving group. Its examples may be methyltrifluoroacetate and ethyltrifluoroacetate, which are easily available in an industrial scale. The solvent for dissolving 1,1,1-trifluoroacetone and the trifluoroacetic acid ester may or may not be the same ether as that for the reaction solvent. As mentioned above, a mixture of 1,1,1-trifluoroacetone, a trifluoroacetic acid ester, and a solvent may be added to the reaction vessel, in view of operability of the reaction. It is, however, not necessary to mix these components to be added to the reaction vessel. Furthermore, this solvent may be omitted. As mentioned above, it is preferable to cool the reaction mixture during the addition of these components in order to prevent the temperature increase. The reaction temperature is preferably about 0-90xc2x0 C., more preferably about 20-70xc2x0 C. If it is lower than 0xc2x0 C., the reaction rate may become too low. If it is higher than 90xc2x0 C., the yield of 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate may become too low.
After the completion of the above reaction, a salt of crude 1,1,1,5,5,5-hexafluoroacetylacetone is obtained by removing the reaction solvent. The removal of the reaction solvent is conducted by applying heat and/or vacuum. After that, the reaction liquid of the residue is put into another reaction vessel, followed by the addition of water and then acid (e.g., sulfuric acid, hydrochloric acid, or nitric acid), thereby decomposing the salt. Then, solvent extraction is conducted by adding a solvent to the reaction liquid. Then, the solvent is removed from the obtained organic layer, thereby obtaining a crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate containing impurities, in the form of solid.
In the first process, the manner of bringing the crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate into contact with a poor solvent is not particularly limited. For example, the crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate may be dispersed in the poor solvent. Then, the precipitated 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate can be separated by filtration. As another example, it is possible to apply the poor solvent as a washing liquid to the crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate supported on a filter of a filtration device. The resulting 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate is usually dried. However, if it is used as a raw material for producing 1,1,1,5,5,5-hexafluoroacetylacetone, the drying is not necessary.
In the second process, it is possible to dissolve the crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate in an organic solvent to form a solution. To this solution it is possible to add a poor solvent, thereby precipitating 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate. Then, this product can be separated by filtration. Alternatively, the above solution can be cooled to reduce solubility, thereby precipitating 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate.
The temperature for conducting the above-mentioned procedures is not particularly limited. It is preferably about 0-90xc2x0 C., more preferably about 20-60xc2x0 C. In view of operability, it is preferably a temperature requiring no heating nor cooling.
The above-mentioned poor solvent used in the first or second process can be selected from hydrocarbons and fluorine-containing solvents free from chlorine. It is needless to say that this poor solvent is in the form of liquid upon its use. This poor solvent is not particularly limited, and its boiling point is preferably not higher than about 200xc2x0 C. Examples of the hydrocarbons are (1) aliphatic hydrocarbons such as n-pentane, n-hexane, n-heptane, n-octane, n-nonane, n-decane and isomers of these, the isomers being in liquid at about 5xc2x0 C.; (2) aromatic hydrocarbons such as benzene, toluene, o-xylene, m-xylene, p-xylene, ethyl benzene, and mesitylene; (3) alicyclic hydrocarbons such as cyclopentane, cyclohexane, methylcyclopentane, methylcyclohexane, tetralin, and decalin; and (4) industrial gasolines (mixtures of hydrocarbon solvents) such as ligroin and petroleum ether. Examples of the fluorine-containing solvents are 1,2-bis(trifluoromethyl)benzene, 1,3-bis(trifluoromethyl)benzene, 1,4-bis(trifluoromethyl)benzene, 1,1,1,3,3-pentafluoropropane, 1,1,1,3,3-pentafluorobutane, heptafluorocyclopentane, and perfluorinated cyclic ethers ( FLORINAT(copyright)). It is possible to use a mixture of at least two of these.
In the first process, it is optional to mix the poor solvent with a small amount of a good solvent in which solubility of 1,1,1,5,5,5-hexafluoroacetylacetone is higher than in the poor solvent. The amount of the good solvent may be not greater than 30 parts by weight per 100 parts by weight of the poor solvent. The good solvent in the invention is not particularly limited. Its examples are ethers such as diethyl ether, dibutyl ether, t-butyl methyl ether, diisopropyl ether, and tetrahydrofuran (THF); and alcohols such as methanol, ethanol, n-propanol, isopropanol, and n-butanol.
In the second process, it is optional to add a poor solvent to the solvent used for preparing the solution of the crude 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate, in order to adjust the solubility in the solution. This addition is particularly preferable, if crystals of 1,1,1,5,5,5-hexafluoroacetylacetone are precipitated by lowering the temperature of the solution.
It is possible to dehydrate 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate, which has been purified in accordance with the invention, by a conventional method, thereby obtaining its anhydride. R. Belford, J. Inorganic and Nuclear Chemistry, 1956, Vol. 2, pp. 11-31 discloses such method in which a dispersion is prepared by shaking 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate with approximately three times its volume of 98% sulfuric acid. After the dispersion has been allowed to stand overnight, dehydration of the product is repeated with a fresh batch of sulfuric acid. The resulting upper layer is siphoned off and distilled, thereby obtaining the anhydride (yield: 98%) as a distillate between 70.0-70.2xc2x0 C. J. Amer. Chem. Soc., 78, 2790 (1956) discloses another method in which anhydrous calcium sulfate is mixed with 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate. Then, the resulting mixture is heated. The distillate is again treated with anhydrous calcium sulfate and distilled, thereby obtaining the anhydride of a boiling point of 68xc2x0 C. (736 mm.). There is known a still another method in which 1,1,1,5,5,5-hexafluoroacetylacetone dihydrate, together with phosphorus pentoxide, is heated in ether.